U.S. patent application number 17/047384 was filed with the patent office on 2021-04-22 for positive electrode composition for lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery.
The applicant listed for this patent is Denka Company Limited. Invention is credited to Tetsuya ITO, Tatsuya NAGAI, Shinichiro OSUMI.
Application Number | 20210119206 17/047384 |
Document ID | / |
Family ID | 1000005339739 |
Filed Date | 2021-04-22 |
![](/patent/app/20210119206/US20210119206A1-20210422-D00000.png)
![](/patent/app/20210119206/US20210119206A1-20210422-D00001.png)
United States Patent
Application |
20210119206 |
Kind Code |
A1 |
NAGAI; Tatsuya ; et
al. |
April 22, 2021 |
POSITIVE ELECTRODE COMPOSITION FOR LITHIUM ION SECONDARY BATTERY,
POSITIVE ELECTRODE FOR LITHIUM ION SECONDARY BATTERY, AND LITHIUM
ION SECONDARY BATTERY
Abstract
A positive electrode composition for a lithium ion secondary
battery includes an active material that can occlude and release
lithium ions and a conductive material, wherein the active material
is a lithium cobalt composite oxide; the conductive material is
carbon black and carbon nanotubes; the carbon black has a BET
specific surface area of 100 to 400 m.sup.2/g and a DBP absorption
amount of 210 to 400 ml/100 g; the carbon nanotubes have an average
diameter of 20 nm or less, a BET specific surface area of 170
m.sup.2/g or more, and an aspect ratio of 50 or more; and a carbon
black content X (unit: % by mass) and a carbon nanotube content Y
(unit: % by mass) in the positive electrode composition satisfy the
following conditions (A) and (B): (A) 0.5.ltoreq.(X+Y).ltoreq.2.0;
(B) 0.80.ltoreq.{X/(X+Y)}.ltoreq.0.95.
Inventors: |
NAGAI; Tatsuya; (Chiba,
JP) ; OSUMI; Shinichiro; (Tokyo, JP) ; ITO;
Tetsuya; (Chiba, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Denka Company Limited |
Tokyo |
|
JP |
|
|
Family ID: |
1000005339739 |
Appl. No.: |
17/047384 |
Filed: |
April 26, 2019 |
PCT Filed: |
April 26, 2019 |
PCT NO: |
PCT/JP2019/017989 |
371 Date: |
October 13, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/131 20130101;
H01M 2004/028 20130101; H01M 4/133 20130101; H01M 10/0525 20130101;
H01M 4/525 20130101 |
International
Class: |
H01M 4/525 20060101
H01M004/525; H01M 10/0525 20060101 H01M010/0525; H01M 4/133
20060101 H01M004/133; H01M 4/131 20060101 H01M004/131 |
Foreign Application Data
Date |
Code |
Application Number |
May 8, 2018 |
JP |
2018-090074 |
Claims
1. A positive electrode composition for a lithium ion secondary
battery, comprising an active material that can occlude and release
lithium ions and a conductive material, wherein the active material
is a lithium cobalt composite oxide; the conductive material is
carbon black and carbon nanotubes; the carbon black has a BET
specific surface area of 100 to 400 m.sup.2/g and a DBP absorption
amount of 210 to 400 ml/100 g; the carbon nanotubes have an average
diameter of 20 nm or less, a BET specific surface area of 170
m.sup.2/g or more, and an aspect ratio of 50 or more; and a carbon
black content X (unit: % by mass) and a carbon nanotube content Y
(unit: % by mass) in the positive electrode composition satisfy the
following conditions (A) and (B); 0.5.ltoreq.(X+Y).ltoreq.2.0 (A)
0.80.ltoreq.{X/(X+Y)}.ltoreq.0.95. (B)
2. The positive electrode composition for a lithium ion secondary
battery according to claim 1, wherein the lithium cobalt composite
oxide has an average particle diameter D.sub.50 of 10 to 20
.mu.m.
3. The positive electrode composition for a lithium ion secondary
battery according to claim 1, wherein the BET specific surface area
of the carbon nanotubes is larger than 200 m.sup.2/g.
4. The positive electrode composition for a lithium ion secondary
battery according to claim 1, wherein the positive electrode
composition for a lithium ion secondary battery comprises 96% by
mass or more of the lithium cobalt composite oxide.
5. A positive electrode for a lithium ion secondary battery
comprising the positive electrode composition for a lithium ion
secondary battery according to claim 1.
6. A lithium ion secondary battery comprising the positive
electrode for a lithium ion secondary battery according to claim 5.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a positive electrode
composition for a lithium ion secondary battery, a positive
electrode for a lithium ion secondary battery, and a lithium ion
secondary battery.
BACKGROUND OF THE INVENTION
[0002] Due to seriousness environmental and energy problems,
technologies for the realization of a low-carbon society that
reduces dependency on fossil fuels are being actively developed.
Examples of such technological development include the development
of low-emission vehicles such as hybrid electric vehicles and
electric vehicles, the development of renewable energy power
generation and power storage systems such as solar power generation
and wind power generation, the development of a next-generation
power grid that efficiently supplies power and reduces power
transmission loss, which extends to a wide variety.
[0003] One of the key devices commonly required for these
technologies is a battery, and such a battery is required to have a
high energy density for miniaturizing the system. In addition, high
output characteristics are required to enable stable power supply
regardless of the operating environment temperature. Further, good
cycle characteristics that can withstand long-term use are also
required. Therefore, the replacement of conventional lead-acid
batteries, nickel-cadmium batteries, and nickel-hydrogen batteries
with lithium ion secondary batteries which has higher energy
density, output characteristics, and cycle characteristics is
rapidly progressing.
[0004] A basic configuration of such a lithium ion secondary
battery is composed of a positive electrode, a negative electrode,
a separator, and an electrolyte. The positive electrode is
generally composed of a positive electrode active material such as
a lithium composite oxide, a conductive material, a positive
electrode composition containing a binder, and a metal (such as
aluminum) foil current collector. As the conductive material, a
particulate carbon material such as carbon black is generally
used.
[0005] By the way, carbon black has a configuration which primary
particles close to a sphere shape are connected in a rosary-like
shape as a common configuration thereof, and such a configuration
is called a structure. The length of the structure is indirectly
evaluated using the DBP absorption amount measured in accordance
with JIS K6217-4. Generally, when the DBP absorption amount becomes
larger, the structure becomes longer, resulting better effect of
imparting conductivity, and more excellent liquid retention
property, which is the ability to retain non-aqueous electrolyte
solutions.
[0006] In recent years, further improvement of the energy density
of such lithium ion secondary battery has been required. Therefore,
it is required to reduce the content of the conductive material,
which is a component that does not contribute to the
charge/discharge capacity in the electrode, and increase the
content of the active material. As a means for solving this
problem, there has been proposed a technique for using fibrous
carbon material, which has a higher aspect ratio than particulate
carbon material such as carbon black and can impart conductivity
with a smaller amount of addition, in combination with carbon
black.
[0007] Patent Literature 1 discloses a technique in which a carbon
nanofiber electrically bridges an active material and carbon black
to create a good conductive path in an electrode and a battery
having excellent cycle characteristics is obtained. However, when
carbon black having a smaller particle diameter and a longer
structure, which can impart conductivity with a smaller amount of
addition, is used, sufficient conductive paths cannot be formed and
the content of the active material cannot be increased, which is a
problem.
[0008] Patent Literature 2 discloses a technique for obtaining a
battery having excellent output characteristics by preventing the
conductive material from being unevenly distributed in the
electrodes by using carbon black and carbon nanotubes in
combination. Further, in Patent Literature 3, there is disclosed a
technique for obtaining batteries with excellent cycle
characteristics and output characteristics by setting the
proportion of fibrous carbon material to 1 to 20% by weight and the
proportion of granular carbon material to 99 to 80% by weight when
the entire conductive material is 100% by weight so as to improve
the conductivity in the electrode. However, since the technique is
based on the premise that a large amount of conductive material is
added in both inventions, there has been a problem that the content
of the active material cannot be increased.
[0009] Patent Literature 4 discloses a technique for obtaining a
battery having excellent output characteristics and cycle
characteristics by stabilizing the conductive paths in the positive
electrode by using carbon black and graphitized carbon fiber in
combination. Further, Patent Literature 5 discloses a technique for
obtaining a battery having low resistance and excellent discharge
capacity and cycle characteristics by using carbon black and
fibrous carbon in combination. However, in both inventions, since
the fiber diameter of the fibrous carbon material used is large, it
is necessary to add a large amount of the fibrous carbon material
in order to form sufficient conductive paths, and the proportion of
carbon black used in combination will be reduced. As a result,
there has been a problem that retaining a sufficient electrolytic
solution in the vicinity of the active material is impossible, and
sufficient output characteristics cannot be obtained when used in a
low temperature environment.
CITATION LIST
Patent Literature
[Patent Literature 1] WO 2013/179909
[Patent Literature 2] Japanese Unexamined Patent Publication No.
2007-80652
[Patent Literature 3] Japanese Patent Publication No. 11-176446
[Patent Literature 4] Japanese Patent Publication No.
2001-126733
[Patent Literature 5] Japanese Patent Publication No.
2010-238575
SUMMARY OF THE INVENTION
[0010] In view of the above problems and circumstances, the object
of the present invention is to provide a positive electrode
composition for a lithium ion secondary battery capable of easily
obtaining a lithium ion secondary battery having high energy
density, low internal resistance, and excellent output
characteristics, cycle characteristics, and low temperature
characteristics.
[0011] As a result of diligent research, the present inventors have
found that the above problems can be solved by using carbon black
with a small particle diameter and a long structure and carbon
nanotubes with a small fiber diameter and a specific BET specific
surface area and aspect ratio as the conductive materials for a
specific active material.
[0012] Specifically, according to the present invention, a positive
electrode composition for lithium ion secondary battery comprises
lithium cobalt oxide as an active material, carbon black with a
small particle diameter and a long structure, and carbon nanotubes
with a small fiber diameter and a specific BET specific surface
area and aspect ratio as a conductive material. A lithium ion
secondary battery manufactured by using such a positive electrode
composition for a lithium ion secondary battery has a high energy
density, a low internal resistance, and is excellent in output
characteristics, cycle characteristics, and low temperature
characteristics. The present invention is completed based on such
findings.
[0013] Accordingly, the present invention is specified as
follows.
(1) A positive electrode composition for a lithium ion secondary
battery, comprising an active material that can occlude and release
lithium ions and a conductive material, wherein [0014] the active
material is a lithium cobalt composite oxide; [0015] the conductive
material is carbon black and carbon nanotubes; [0016] the carbon
black has a BET specific surface area of 100 to 400 m.sup.2/g and a
DBP absorption amount of 210 to 400 ml/100 g; [0017] the carbon
nanotubes have an average diameter of 20 nm or less, a BET specific
surface area of 170 m.sup.2/g or more, and an aspect ratio of 50 or
more; and [0018] a carbon black content X (unit: % by mass) and a
carbon nanotube content Y (unit: % by mass) in the positive
electrode composition satisfy the following conditions (A) and
(B).
[0018] 0.5.ltoreq.(X+Y).ltoreq.2.0 (A)
0.80.ltoreq.{X/(X+Y)}.ltoreq.0.95 (B)
(2) The positive electrode composition for a lithium ion secondary
battery according to (1), wherein the lithium cobalt composite
oxide has an average particle diameter D.sub.50 of 10 to 20 .mu.m.
(3) The positive electrode composition for a lithium ion secondary
battery according to (1) or (2), wherein the BET specific surface
area of the carbon nanotubes is larger than 200 m.sup.2/g. (4) The
positive electrode composition for a lithium ion secondary battery
according to any one of (1) to (3), wherein the positive electrode
composition for a lithium ion secondary battery comprises 96% by
mass or more of the lithium cobalt composite oxide. (5) A positive
electrode for a lithium ion secondary battery comprising the
positive electrode composition for a lithium ion secondary battery
according to any one of (1) to (4). (6) A lithium ion secondary
battery comprising the positive electrode for a lithium ion
secondary battery according to (5).
[0019] According to the present invention, it is possible to
provide a positive electrode composition for a lithium ion
secondary battery capable of easily obtaining a lithium ion
secondary battery having high energy density, low internal
resistance, and excellent output characteristics, cycle
characteristics, and low temperature characteristics.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic perspective view showing the structure
of a test battery used in Examples and Comparative Examples.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Hereinafter, the present invention will be described in
detail. The positive electrode composition for a lithium ion
secondary battery according to the present invention comprises an
active material and a conductive material, wherein the active
material is a lithium cobalt composite oxide; the conductive
material is carbon black and carbon nanotubes; the carbon black has
a BET specific surface area of 100 to 400 m.sup.2/g and a DBP
absorption amount of 210 to 400 ml/100 g; the carbon nanotubes have
an average diameter of 20 nm or less, a BET specific surface area
of 170 m.sup.2/g or more, and an aspect ratio of 50 or more.
[0022] As the lithium cobalt composite oxide which is the active
material according to the present invention, for example, lithium
cobalt oxide can be used. As the lithium cobalt oxide, those
produced by conventionally known methods such as a solid phase
method, a liquid phase method, and a vapor phase method may be
used, similar to lithium cobalt oxide generally used as an active
material for a battery. Further, active material whose surface is
coated with a metal oxide such as ZrO.sub.2, Al.sub.2O.sub.3,
TiO.sub.2, SiO.sub.2, MgO, TiO.sub.2, or Li.sub.2CO.sub.3,
AlF.sub.3 or the like also may be used. In addition to lithium
cobalt oxide, other active materials may be included as long as the
effects of the present invention are not impaired.
[0023] The average particle diameter D.sub.50 of the lithium cobalt
composite oxide such as lithium cobalt oxide according to the
present invention is preferably 10 to 20 .mu.m. By setting the
average particle diameter in such a range, the filling rate of the
active material in the obtained positive electrode is improved, and
it becomes easy to obtain a positive electrode having a high energy
density. Further, it becomes easy to bring out the features of the
conductive material described later, and it becomes easy to obtain
a high output battery with an extremely small amount of the
conductive material added. Further, when the obtained battery is
charged and discharged, the decomposition of the electrolytic
solution is suppressed, and good cycle characteristics can be
easily obtained. The average particle diameter according to the
present invention is a value obtained by dispersing the positive
electrode active material using ethanol as a dispersion medium and
measuring it with a laser diffraction/scattering type particle
diameter distribution measuring device in accordance with JIS
Z8825. In addition, The content of the lithium cobalt composite
oxide such as lithium cobalt oxide according to the present
invention is preferably 96% by mass or more with respect to the
positive electrode composition which may comprise the lithium
cobalt oxide, the conductive material and a binder. With such a
content, it becomes easy to obtain a battery having a sufficiently
high energy density.
[0024] The conductive material according to the present invention
is carbon black and carbon nanotubes. Carbon black is selected from
acetylene black, furnace black, channel black, and the like,
similar to carbon black generally used as conductive material for
batteries. Of these, acetylene black, which has excellent
crystallinity and purity, is preferable. In addition to carbon
black and carbon nanotubes, other conductive materials may be
included as long as the effects of the present invention are not
impaired.
[0025] The BET specific surface area of the carbon black according
to the present invention is 100 to 400 m.sup.2/g. By setting the
BET specific surface area to 100 m.sup.2/g or more, the number of
electrical contacts with the active material and the current
collector is increased, and a good conductivity-imparting effect
can be obtained. Further, by setting the content to 400 m.sup.2/g
or less, the interaction between the particles is suppressed, so
that the particles are uniformly dispersed in the positive
electrode active materials, and good conductive paths can be
obtained. From this viewpoint, the BET specific surface area of the
carbon black is more preferably 120 to 380 m.sup.2/g. The BET
specific surface area according to the present invention is a value
measured by the static volume method in accordance with JIS Z 8830,
using nitrogen as an adsorbent.
[0026] The DBP absorption amount of the carbon black according to
the present invention is 210 to 400 ml/100 g. By setting the DBP
absorption amount to 210 ml/100 g or more, when it is used as the
conductive material, the structure has a sufficient length and
spread, and a good conductive paths and liquid retention property
of a non-aqueous electrolytic solutions can be obtained. Further,
by setting the amount to 400 ml/100 g or less, aggregation due to
entanglement between structures is suppressed, so that the
structures are uniformly dispersed in the positive electrode active
materials, so that it is possible to achieve both the formation of
good conductive paths and sufficient liquid retention for
non-aqueous electrolyte solutions. From this viewpoint, the DBP
absorption amount of the carbon black is more preferably 250 to 320
ml/100 g. The DBP absorption amount according to the present
invention is the value measured in accordance with JIS K6217-4.
[0027] The volume resistivity of carbon black according to the
present invention is not particularly limited, but it is preferable
that it is low from the viewpoint of conductivity. Specifically,
the volume resistivity measured under 7.5 MPa compression is
preferably 0.30 .OMEGA.cm or less, and more preferably 0.25
.OMEGA.cm or less.
[0028] The ash content and water content of carbon black according
to the present invention are not particularly limited, but from the
viewpoint of suppressing side reactions, it is preferable that both
of them are small. Specifically, the ash content is preferably
0.04% by mass or less, and the water content is preferably 0.10% by
mass or less.
[0029] For the carbon nanotubes according to the present invention,
the average diameter is 20 nm or less, the BET specific surface
area is 170 m.sup.2/g or more, and the aspect ratio is 50 or more.
By setting the average diameter to 20 nm or less and the BET
specific surface area to 170 m.sup.2/g or more, the number of
electrical contacts with the surface of the active material is
increased, and good conductive paths can be obtained. From this
viewpoint, it is more preferable that the average diameter of the
carbon nanotubes is 15 nm or less and the BET specific surface area
is larger than 200 m.sup.2/g. Further, by setting the aspect ratio
to 50 or more, it is possible to efficiently form conductive paths
with few interruptions on the surface of the active material. From
this point of view, the aspect ratio of the carbon nanotubes is
more preferably 100 or more. The average diameter and aspect ratio
according to the present invention are shapes measured by an image
analysis method using a transmission electron microscope, a
reflection electron microscope, an optical microscope, or the like.
Specifically, they are sizes represented by the average value of 20
carbon nanotubes. In addition, the aspect ratio is the ratio of
average length/average diameter. Further, the BET specific surface
area according to the present invention is a value measured by the
static volume method in accordance with JIS Z 8830, using nitrogen
as an adsorbent.
[0030] The carbon black content X (unit: % by mass) and the carbon
nanotube content Y (unit: % by mass) according to the present
invention satisfy 0.5.ltoreq.(X+Y).ltoreq.2.0 and
0.80.ltoreq.{X/(X+Y)}.ltoreq.0.95. By setting
0.5.ltoreq.(X+Y).ltoreq.2.0, a sufficient effect of imparting
conductivity can be obtained while keeping the content of the
conductive material, which is a component that does not contribute
to the charge/discharge capacity, low in the positive electrode
composition. Further, by setting 0.80.ltoreq.{X/(X+Y)}.ltoreq.0.95,
carbon black forms conductive paths between active materials in the
positive electrode composition and retains a non-aqueous
electrolytic solution in the vicinity of the active material, so
that an electrode structure is formed in which carbon nanotubes
play a role in forming conductive paths on the surface of the
active material. The electrode thus obtained has both good
conductive paths and ionic transport paths, and good battery
characteristics can be obtained when used in a battery. From the
above viewpoint, X+Y is more preferably 0.9 or more, and more
preferably 1.3 or less.
[0031] The manufacturing of the positive electrode composition for
a lithium ion secondary battery according the present invention is
not particularly limited, and a conventionally known method can be
used. For example, a solvent dispersion solution of a positive
electrode active material, a conductive material, and a binder is
obtained by mixing with a ball mill, sand mill, twin-screw kneader,
rotating/revolving stirrer, planetary mixer, dispenser mixer, or
the like, and is generally manufactured and used in the state of a
dispersion liquid in which it is dispersed in a dispersion medium.
As the positive electrode active material and the conductive
material, those described above may be used. The carbon black and
the carbon nanotubes may be put into a mixer separately or may be
mixed in advance. Examples of the binder include polymers such as
polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene
copolymer, polyvinyl alcohol, acrylonitrile-butadiene copolymer,
carboxylic acid-modified (meth) acrylic acid ester copolymer, and
the like. Of these, polyvinylidene fluoride is preferable in terms
of oxidation resistance. Examples of the dispersion medium include
water, N-methyl-2-pyrrolidone, cyclohexane, methyl ethyl ketone,
methyl isobutyl ketone and the like. When polyvinylidene fluoride
is used as a binder, N-methyl-2-pyrrolidone is preferable in terms
of solubility.
[0032] In addition, the positive electrode composition for a
lithium ion secondary battery according to the present invention
may comprise components other than the positive electrode active
material, the conductive material, and the binder as long as the
effects of the present invention are not impaired. For example,
polyvinylpyrrolidone, polyvinylimidazole, polyethylene glycol,
polyvinyl alcohol, polyvinyl butyral, carboxymethyl cellulose,
acetyl cellulose, carboxylic acid-modified (meth) acrylic acid
ester copolymer, or the like may be comprised for the purpose of
improving dispersibility.
[0033] The method for manufacturing a positive electrode for a
lithium ion secondary battery according to the present invention is
not particularly limited, and a conventionally known method for
manufacturing a positive electrode may be used. For example, a
positive electrode can be manufactured by the following method.
That is, after the above-mentioned dispersion liquid is applied
onto a metal (such as aluminum) foil current collector, the
dispersion medium contained in the positive electrode composition
according to the present invention is removed by heating, so that a
positive electrode is obtained by forming a film of the positive
electrode composition for a secondary battery on the surface of the
current collector. Further, the target electrode can be obtained by
pressing the current collector and an electrode mixture layer with
a roll press or the like to bring them into close contact with each
other.
[0034] The method for manufacturing the lithium ion secondary
battery according to the present invention is not particularly
limited, and a conventionally known method for manufacturing a
secondary battery may be used, but for example, it can also be
manufactured by the following method. That is, it can be made by
arranging a polyolefin microporous membrane as an insulating layer
between the positive electrode and the negative electrode, and
injecting a non-aqueous electrolytic solution into the voids of the
positive electrode, the negative electrode and the polyolefin
microporous membrane until the non-aqueous electrolytic solution is
sufficiently impregnated.
[0035] The lithium ion secondary battery according to the present
invention is not particularly limited, but can be used in a wide
range of fields, for example, portable AV devices such as digital
cameras, video cameras, portable audio players, portable LCD TVs,
mobile information terminals such as laptop computers, smartphones,
mobile PCs, and portable game devices, electric tools, electric
bicycles, hybrid vehicles, electric cars, power storage systems,
and the like.
EXAMPLES
[0036] Hereinafter, the positive electrode composition for a
lithium ion secondary battery according to the present invention
will be described in detail with reference to Examples and
Comparative Examples. However, the present invention is not limited
to the following examples as long as the spirit of the present
invention is not exceeded.
Example 1
(Positive Electrode Composition for Lithium Ion Secondary
Battery)
[0037] Lithium cobalt oxide (manufactured by Yumicore, "KD-20")
LiCoO.sub.2 with an average particle diameter D.sub.50 of 20 .mu.m
as an active material, and carbon black with a BET specific surface
area of 370 m.sup.2/g and a DBP absorption amount of 310 ml/100 g
(manufactured by Denka, "SAB", described as acetylene black-A in
Table 1) and a N-Methylpyrrolidone dispersion of carbon nanotubes
with an average diameter of 9 nm and a BET specific surface area of
243 m.sup.2/g (manufactured by CNano, "LB107") as conductive
materials, are prepared. To the lithium cobalt oxide 98.4% by mass,
the carbon black 0.76% by mass, and the carbon nanotubes with a
dispersed mass of 0.04% by mass, a N-methylpyrrolidone solution of
polyvinylidene fluoride as a binder with a dissolved mass of 0.8%
by mass, and N-methylpyrrolidone as a dispersion medium, were added
and mixed. A dispersion of a positive electrode composition for a
lithium ion secondary battery was thus obtained.
(Positive Electrode for Lithium Ion Secondary Battery)
[0038] The dispersion liquid of the positive electrode composition
for a lithium ion secondary battery was applied to an aluminum foil
having a thickness of 20 .mu.m using a baker type applicator,
dried, and then pressed and cut to obtain a positive electrode for
a lithium ion secondary battery.
(Negative Electrode for Lithium Ion Secondary Battery)
[0039] A negative electrode composition for a lithium ion secondary
battery (graphite (manufactured by Shenzhen BTR, "AGP-2A") 95% by
mass, carbon black (manufactured by Denka, "Li-400") 1.0% by mass,
polyvinylidene fluoride 1.5% by mass, and styrene-butadiene
copolymer 2.5% by mass) was applied to an copper foil having a
thickness of 20 .mu.m using a baker type applicator, dried, and
then pressed and cut to obtain a positive electrode for a lithium
ion secondary battery.
(Lithium Ion Secondary Battery)
[0040] The positive electrode, a separator, and the negative
electrode were overlapped and laminated together, and then packed
and pre-sealed with an aluminum laminate film, and then an
electrolytic solution was injected, and battery formatting and
vacuum sealing were performed to obtain a laminated lithium ion
secondary battery.
[Internal Resistance]
[0041] The prepared lithium ion secondary battery was
charged/discharged for 5 cycles in a voltage range of 2.75 to 4.2
V, and then impedance analysis was performed in a frequency range
of 10 MHz to 0.001 Hz and a vibration voltage of 5 mV. The internal
resistance of this Example was 1.620.
[Output Characteristics (Capacity Retention Rate at the Time of 3 C
Discharge)]
[0042] The prepared lithium ion secondary battery was charged at a
constant current constant voltage limited to 4.2 V and 0.2 C at
25.degree. C., and then discharged to 2.75 V at a constant current
of 0.2 C. Next, the discharge current was changed to 0.2 C and 3 C,
and the discharge capacity for each discharge current was measured.
Then, the capacity retention rate at the time of 3 C discharge with
respect to the time of 0.2 C discharge was calculated. The capacity
retention rate at the time of 3 C discharge in this Example was
96.8%.
[Cycle Characteristics (Cycle Capacity Retention Rate)]
[0043] The prepared lithium ion battery was charged at a constant
current constant voltage limited to 4.2 V and 1 C at 25.degree. C.,
and then discharged to 2.75 V at a constant current of 1 C. The
charge and discharge cycles were repeated, and the ratio of the
discharge capacity at the 500th cycle to the discharge capacity at
the first cycle was obtained and used as the cycle capacity
retention rate. The cycle capacity retention rate in this Example
was 96.2%.
[Low Temperature Output Characteristics (Capacity Retention Rate
when Discharged at -20.degree. C.)]
[0044] The prepared lithium ion secondary battery was charged at a
constant current constant voltage of 4.2 V and 0.2 C limit at
25.degree. C., and then discharged to 2.75 V at a constant current
of 0.5 C. Next, after charging with a constant current constant
voltage limited to 4.2 V and 0.2 C at -20.degree. C., the battery
was discharged to 2.75 V at a constant current of 0.5 C. Then, the
capacity retention rate at the time of -20.degree. C. discharge
with respect to the time of 25.degree. C. discharge was calculated.
The capacity retention rate at -20.degree. C. discharge in this
Example was 68.7%.
Example 2
[0045] The carbon black of Example 1 was changed to a carbon black
having a BET specific surface area of 133 m.sup.2/g and a DBP
absorption amount of 270 ml/100 g (manufactured by Denka, "Li-435",
described as acetylene black-B in Table 1), and the content was
changed to 0.9% by mass. The dispersed mass of the carbon nanotube
dispersion was changed to 0.10% by mass, and the dissolved mass of
the polyvinylidene fluoride solution was changed to 1.0% by mass.
Except for these, a dispersion of a positive electrode composition
for a lithium ion secondary battery, a positive electrode for a
lithium ion secondary battery, and a lithium ion secondary battery
were prepared in the same manner as in Example 1, and each
evaluation was performed. The results are shown in Table 1.
Example 3
[0046] The active material of Example 2 was changed to lithium
cobaltate (manufactured by Yumicore Co., Ltd., "KD-10") having an
average particle diameter D.sub.50 of 10 .mu.m. The carbon black
content was changed by 1.2% by mass. The carbon nanotubes were
changed to a N-Methylpyrrolidone dispersion of carbon nanotubes
with an average diameter of 15 nm and a BET specific surface area
of 207 m.sup.2/g (manufactured by CNano, "LB100", listed as CNT-B
in Table 1), and the dispersed mass was changed to 0.3% by mass.
The dissolved mass of the polyvinylidene fluoride solution was
changed to 1.5% by mass. Except for these, a dispersion of a
positive electrode composition for a lithium ion secondary battery,
a positive electrode for a lithium ion secondary battery, and a
lithium ion secondary battery were prepared in the same manner as
in Example 2, and each evaluation was performed. The results are
shown in Table 1.
Example 4
[0047] The active material of Example 2 was changed to lithium
cobaltate (manufactured by Nippon Kagaku Kogyo Co., Ltd., "Celseed
C-5") having an average particle size D.sub.50 of 5 .mu.m. The
carbon black content was changed to 1.8% by mass. The dispersed
mass of the carbon nanotube dispersion was changed to 0.2% by mass,
and the dissolved mass of the polyvinylidene fluoride solution was
changed to 2.0% by mass. Except for these, a dispersion of a
positive electrode composition for a lithium ion secondary battery,
a positive electrode for a lithium ion secondary battery, and a
lithium ion secondary battery were prepared in the same manner as
in Example 2, and each evaluation was performed. The results are
shown in Table 1.
Comparative Example 1
[0048] The content of the carbon black in Example 2 was changed to
2.0% by mass, the dispersed mass of the carbon nanotube dispersion
was changed to 0% by mass, and the dissolved mass of the
polyvinylidene fluoride solution was changed to 2.0% by mass.
Except for these, a dispersion of a positive electrode composition
for a lithium ion secondary battery, a positive electrode for a
lithium ion secondary battery, and a lithium ion secondary battery
were prepared in the same manner as in Example 2, and each
evaluation was performed. The results are shown in Table 1.
Comparative Example 2
[0049] The content of the carbon black in Example 2 was changed to
0% by mass, the dispersed mass of the carbon nanotube dispersion
was changed to 2.0% by mass, and the dissolved mass of the
polyvinylidene fluoride solution was changed to 2.0% by mass.
Except for these, a dispersion of a positive electrode composition
for a lithium ion secondary battery, a positive electrode for a
lithium ion secondary battery, and a lithium ion secondary battery
were prepared in the same manner as in Example 2, and each
evaluation was performed. The results are shown in Table 1.
Comparative Example 3
[0050] The content of the carbon black in Example 2 was changed to
0.7% by mass, the dispersed mass of the carbon nanotube dispersion
was changed to 0.3% by mass. Except for these, a dispersion of a
positive electrode composition for a lithium ion secondary battery,
a positive electrode for a lithium ion secondary battery, and a
lithium ion secondary battery were prepared in the same manner as
in Example 2, and each evaluation was performed. The results are
shown in Table 1.
Comparative Example 4
[0051] The carbon black of Example 2 was changed to a carbon black
having a BET specific surface area of 58 m.sup.2/g and a DBP
absorption amount of 200 ml/100 g (manufactured by Denka, "Li-250",
described as acetylene black-C in Table 1). Except for this, a
dispersion of a positive electrode composition for a lithium ion
secondary battery, a positive electrode for a lithium ion secondary
battery, and a lithium ion secondary battery were prepared in the
same manner as in Example 2, and each evaluation was performed. The
results are shown in Table 1.
Comparative Example 5
[0052] The carbon black of Example 2 was changed to a carbon black
having a BET specific surface area of 877 m.sup.2/g and a DBP
absorption amount of 390 ml/100 g (manufactured by Lion, "ECP",
described as carbon black-A in Table 1), and the content was
changed to 0.4% by mass. The dispersed mass of the carbon nanotube
dispersion was changed to 1.6% by mass, and the dissolved mass of
the polyvinylidene fluoride solution was changed to 2.0% by mass.
Except for these, a dispersion of a positive electrode composition
for a lithium ion secondary battery, a positive electrode for a
lithium ion secondary battery, and a lithium ion secondary battery
were prepared in the same manner as in Example 2, and each
evaluation was performed. The results are shown in Table 1.
Comparative Example 6
[0053] The carbon black of Example 2 was changed to a carbon black
having a BET specific surface area of 877 m.sup.2/g and a DBP
absorption amount of 390 ml/100 g (manufactured by Lion, "ECP",
described as carbon black-A in Table 1), and the content was
changed to 0.9% by mass. The dispersed mass of the carbon nanotube
dispersion was changed to 0.1% by mass, and the dissolved mass of
the polyvinylidene fluoride solution was changed to 1.0% by mass.
Except for these, a dispersion of a positive electrode composition
for a lithium ion secondary battery, a positive electrode for a
lithium ion secondary battery, and a lithium ion secondary battery
were prepared in the same manner as in Example 2, and each
evaluation was performed. The results are shown in Table 1.
Comparative Example 7
[0054] The carbon nanotubes of Example 2 were changed to carbon
nanotubes having an average diameter of 25 nm and a BET specific
surface area of 100 m.sup.2/g (manufactured by Wako Chemical Co.,
Ltd., described as CNT-C in Table 1). Except for these, a
dispersion of a positive electrode composition for a lithium ion
secondary battery, a positive electrode for a lithium ion secondary
battery, and a lithium ion secondary battery were prepared in the
same manner as in Example 2, and each evaluation was performed. The
results are shown in Table 1.
Comparative Example 8
[0055] The active material of Example 2 was changed to lithium
nickel cobalt manganese composite oxide
LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2 (manufactured by Jiangxi
Jiangte Lithium Battery Materials, "L532") having an average
particle diameter D.sub.50 of 8 .mu.m. The content of the carbon
black was changed to 1.8% by mass, the dispersed mass of the carbon
nanotube dispersion was changed to 0.2% by mass, and the dissolved
mass of the polyvinylidene fluoride solution was changed to 2.0% by
mass. Except for these, a dispersion of a positive electrode
composition for a lithium ion secondary battery, a positive
electrode for a lithium ion secondary battery, and a lithium ion
secondary battery were prepared in the same manner as in Example 2,
and each evaluation was performed. The results are shown in Table
1.
TABLE-US-00001 TABLE 1 Comparative Comparative Material Evaluation
item Example 1 Example 2 Example 3 Example 4 Example 1 Example 2
Active Type LCO LCO LCO LCO LCO LCO material Particle diameter D50
(.mu.m) 20 20 10 5 20 20 Carbon Type Acetylene Acetylene Acetylene
Acetylene Acetylene -- black Black-A Black-B Black-B Black-B
Black-B Specific surface area (m.sup.2/g) 370 133 133 133 133 --
DBP absorption amount (mL/100g) 310 270 270 270 270 -- Carbon Type
CNT-A CNT-A CNT-B CNT-A -- CNT-A nanotube Average diameter (nm) 9 9
15 9 -- 9 BET Specific surface area (m.sup.2/g) 243 243 207 243 --
243 Aspect ratio 50 or more 50 or more 50 or more 50 or more -- 50
or more Evaluation X + Y 0.8 10 1.5 2.0 2.0 2.0 X/(X + Y) 0.95 0.90
0.80 0.90 1.00 0 Active material ration (%) in positive 98.4 98.0
97.0 96.0 96.0 96.0 electrode composition Internal resistance
(.OMEGA.) 1.62 1.56 1.82 2.35 3.26 3.67 Capacity retention rate (%)
at time 96.8 97.3 95.0 91.3 83.2 76.1 of 3 C discharge Cycle
capacity retention rate (%) 96.2 97.2 94.1 90.6 8S.3 90.5 Capacity
retention rate (%) when 68.7 68.8 65.8 60.4 55.1 46.8 discharged at
-20.degree. C. Comparative Comparative Comparative Comparative
Comparative Comparative Material Evaluation item Example 3 Example
4 Example 5 Example 6 Example 7 Example 8 Active Type LCO LCO LCO
LCO LCO NMC material Particle diameter D50 (.mu.m) 20 20 20 20 20 8
Carbon Type Acetylene Acetylene Carbon Carbon Acetylene Acetylene
black Black-B Black-C Black-A Black-A Black-B Black-B Specific
surface area (m.sup.2/g) 133 58 877 877 133 133 DBP absorption
amount (mL/100 g) 270 200 390 390 270 270 Carbon Type CNT-A CNT-A
CNT-A CNT-A CNT-C CNT-A nanotube Average diameter (nm) 9 9 9 9 25 9
BET Specific surface area (m.sup.2/g) 243 243 243 243 100 243
Aspect ratio 50 or more 50 or more 50 or more 50 or more 40 50 or
more Evaluation X + Y 1.0 1.0 2.0 1.0 1.0 2.0 X/(X + Y) 0.70 0.90
0.20 0.90 0.90 0.90 Active material ration (%) in positive 98.0
98.0 96.0 98.0 98.0 96.0 electrode composition Internal resistance
(.OMEGA.) 3.42 4.34 5.39 3.47 4.72 4.6 Capacity retention rate (%)
at time 81.3 72.6 62.7 73.2 68.7 81.2 of 3 C discharge Cycle
capacity retention rate (%) 88.7 88.3 86.2 87.3 81.4 82.4 Capacity
retention rate (%) when 52.6 51.8 47.3 50.8 53.1 50.3 discharged at
-20.degree. C.
[0056] From the results in Table 1, it can be understood that the
lithium ion secondary batteries prepared by using the positive
electrode compositions for a lithium ion secondary battery
according to the present invention had a high energy density, a low
internal resistance, and is excellent in output characteristics,
cycle characteristics, and low temperature characteristics.
DESCRIPTION OF REFERENCE NUMERALS
[0057] 1 Positive electrode [0058] 2 Negative electrode [0059] 3
Positive electrode aluminum tab [0060] 4 Negative electrode nickel
tab [0061] 5 Polyolefin microporous membrane
* * * * *